title: The Keap1/Nrf2 protein axis plays a role in osteoclast differentiation by regulating intracellular reactive oxygen species signaling.
abstract: Reactive oxygen species (ROS) act as intracellular signaling molecules in the regulation of receptor activator of nuclear factor-κB ligand (RANKL)-dependent osteoclast differentiation, but they also have cytotoxic effects that include peroxidation of lipids and oxidative damage to proteins and DNA. Cellular protective mechanisms against oxidative stress include transcriptional control of cytoprotective enzymes by the transcription factor, nuclear factor E2-related factor 2 (Nrf2). This study investigated the relationship between Nrf2 and osteoclastogenesis. Stimulation of osteoclast precursors (mouse primary peritoneal macrophages and RAW 264.7 cells) with RANKL resulted in the up-regulation of kelch-like ECH-associated protein 1 (Keap1), a negative regulator of Nrf2. It also decreased the Nrf2/Keap1 ratio, and it down-regulated cytoprotective enzymes (heme oxygenase-1, γ-glutamylcysteine synthetase, and glucose-6-phosphate dehydrogenase). Nrf2 overexpression up-regulated the expression of cytoprotective enzymes, decreased ROS levels, decreased the number of tartrate-resistant acid phosphatase-positive multinucleated cells, reduced marker genes for osteoclast differentiation, and attenuated bone destruction in both in vitro and in vivo models. Overexpression of Keap1 or RNAi knockdown of Nrf2 exerted the opposite actions. In addition, in vivo local Nrf2 overexpression attenuated lipopolysaccharide-mediated RANKL-dependent cranial bone destruction in vivo. This is the first study to show that the Keap1/Nrf2 axis regulates RANKL-dependent osteoclastogenesis through modulation of intracellular ROS signaling via expression of cytoprotective enzymes. This raises the exciting possibility that the Keap1-Nrf2 axis may be a therapeutic target for the treatment of bone destructive disease.
authors.affiliation: Maxillo-Oral Disorders, Department of Oral and Maxillofacial Surgery, Tohoku University Hospital, Sendai 980-8575, Japan. kanzaki@dent.tohoku.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kanzaki
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Shinohara
authors.forename: Mikihito
authors.initials: M
authors.lastname: Kajiya
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Kodama
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D000072019:Kelch-Like ECH-Associated Protein 1; D008070:Lipopolysaccharides / Q000494:pharmacology; D017737:Macrophages, Peritoneal / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D010010:Osteoclasts / Q000378:metabolism* / Q000473:pathology; D010014:Osteolysis / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D053245:RANK Ligand / Q000096:biosynthesis; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; C117301:Keap1 protein, mouse; D000072019:Kelch-Like ECH-Associated Protein 1; D008070:Lipopolysaccharides; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D053245:RANK Ligand; D017382:Reactive Oxygen Species; C505689:Tnfsf11 protein, mouse
keywords: Arthritis; Bone; Nrf2; Osteoclast; Periodontal Disease; Reactive Oxygen Species (ROS)